Rapid and high precision centroiding method and system for spots image

ABSTRACT

The disclosure relates to a rapid and high precision centroiding method for spots image comprising the following steps. First, the method requires convoluting the gray value of a pixel with a Gaussian filter and judging whether the result thereof exceeds a predetermined threshold. If the value exceeds the predetermined threshold, the method requires marking the current pixel with a flag to identify which spot it belongs to, and then accumulating the product of the gray value and a coordinate value of the same spot; and at the same time, accumulating the gray value of the same spot; and saving the results of the accumulation respectively. If the gray value of the pixel does not exceed the predetermined threshold, the method requires marking the current pixel as a background flag. After all pixels of the image has been disposed of completely, the method includes calculating a quotient of the accumulations of the product of the gray value and the coordinate value and the accumulations of the gray value, and outputting the quotients. At the same time, a centroiding system for spots image is also presented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Chinese Patent Application Serial No. 200610161802.6 filed Dec. 1, 2006, the disclosure of which, including the specification, drawings and claims, is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to measurement technology of machine vision. In particular, the disclosure relates to a rapid and high precision centroiding method and system for spots image.

BACKGROUND

Spots image is the common image information in the field of machine vision and pattern recognition. The character of the spot image is the center of the spot. The spot center is widely used in object tracking in machine vision, high accuracy 3D measurement in vision and celestial navigation.

At present, there are two known methods of locating the center of the spot's image, one is based on the gray value of the pixels, and another is based on the edge. The information of the distribution of the gray value of the spots image is made use by a locating method which is based on the gray value, such as a centroiding algorithm and a curved surface fitting, method etc. The information regarding the shape of the edge is always used by the locating method which is based on the edge, including circle fitting, Hough transform etc.

The method which is based on the gray value has higher accuracy than the method which is based on the edge. Usually, the method of curved surface fitting fits the gray value distribution of the spots image by a 2D Gaussian curved surface, so the method is too complicated. The centroiding algorithm is used most frequently, due to its easy implementation and its high precision. The centroiding algorithm has some improved forms, mainly including the centroiding algorithm with a threshold value and the square weighted centroiding algorithm. The centroiding algorithm with threshold value is to subtract the background threshold from the original image, calculating the centroiding of the pixels which exceeds the threshold value. The square weighted centroiding algorithm uses the square of the gray value to replace the gray value and highlights the influence of the gray value nearer to the center of the spot.

In the prior art, for real-time application in vision dynamic tracking and the requirement of miniaturization in space application, spot centroiding which is to handle a mass of data and the processing exists in parallel, including operation parallelism, image parallelism, neighborhood parallelism, the pixel position parallelism and so on. But at present, the method of the spot centroiding is implemented mostly by the software in the computer. The implementation is done by instruction and is serial, so spot centroiding becomes the bottleneck of the image processing. For real-time spot centroiding, the system of on-chip windowed centroiding is proposed by Jet Propulsion Laboratory (“JPL”), neuro-MOS circuits have been implemented and integrated with a complementary metal oxide semiconductor (“CMOS”) active pixel sensor (“APS”). More than two windows are set to locate spots centroid at the same time by the system. But due to the analog circuit and windowed processing, some disadvantages are as follows:

1) The window can not be set too large otherwise when more than two spots exist in one window, the two spots will be calculated as one spot which will skew the result with this error. Thus, the approximate position and the range must be known ahead to set the window.

2) Because of the limitation of the process and transmission speed, the number of windows can not be too much, so some spot's centroid can not be calculated

3) Because of implementation with the analog circuit, the centroiding algorithm is sensitive to noise which is the source of the error thereof.

SUMMARY

An embodiment of the present disclosure provides a rapid and high precision centroiding method for spots image, which improves the speed of data processing and the ability of noise-resistance and processing any size and any number of spots.

An embodiment of this disclosure also provides a rapid and high precision centroiding system for spots image, which reduces the bottleneck of image preprocessing and the problem of noise sensitivity. Further, the disclosure also describes a system that processes any size and any number of spots in real-time.

For these purposes, in one embodiment of the disclosure, a method is disclosed for rapid and high precision centroiding for spots image. First, the method requires convoluting the gray value of a pixel with a Gaussian filter and judging whether the result thereof exceeds a predetermined threshold. If the value exceeds the predetermined threshold, the method requires marking the current pixel with a flag to identify which spot it belongs to, and then accumulating the product of the gray value and a coordinate value of the same spot; and at the same time, accumulating the gray value of the same spot; and saving the results of the accumulation respectively. If the gray value of the pixel does not exceed the predetermined threshold, the method requires marking the current pixel as a background flag. After all pixels of the image have been disposed of completely, the method includes calculating a quotient of the accumulations of the product of the gray value and the coordinate value and the accumulations of the gray value, and outputting the quotients. At the same time, a centroiding system for spots image is also presented.

A rapid and high precision centroiding system for spots image is also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of specification, illustrate an exemplary embodiment of the present invention and, together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the present invention.

FIG. 1 illustrates a flowchart of centroiding for spots image;

FIG. 2 illustrates a flowchart for marking pixels according to the process flow set forth in FIG. 1;

FIG. 3 is a schematic drawing of spots images that are marked;

FIG. 4 illustrates a flowchart for merging equivalent flags according to the process flow set forth in FIG. 1;

FIG. 5 is a schematic drawing of a spots image from FIG. 31 of which the equivalent flags are merged;

FIG. 6 is a schematic drawing of an embodiment of a centroiding system for spots image.

DETAILED DESCRIPTION

While the claims are not limited to the illustrated embodiments, an appreciation of various aspects of the present invention is best gained through a discussion of various examples thereof. Referring now to the drawings, illustrative embodiments will be described in detail. Although the drawings represent the embodiments, the drawings are not necessarily to scale and certain features may be exaggerated to better illustrate and explain an innovative aspect of an embodiment. Further, the embodiments described herein are not intended to be exhaustive or otherwise limiting or restricting to the precise form and configuration shown in the drawings and disclosed in the following detailed description.

The principle of this disclosure is as follows. First, a gray value of a pixel of output from a sensor is convoluted with a Gaussian filter. By marking and calculating each pixel of the output image correspondingly, one or more spots images can be automatically identified and disposed of quickly.

The steps of marking and calculating are as follows. First, each output pixel is compared with a predetermined threshold and marked. Next, equivalent flags that belong to the same spots are merged together if it is necessary to guarantee that each pixel of the same spots have the same flag. The product of the gray value and a coordinate value of the pixels are summed together when marking and merging. After processing all pixels of the image, a quotient of the product of the gray value and the coordinate value of the gray value of pixels is calculated, then the results is output as a coordinate of a spot centroid. Thus, rapid and high precision centroiding is realized for any shape and any number spots

The centroiding process of the prior art shows that noise may greatly influence the precision of the process, so Gaussian weighing is used in the present disclosure. More specifically, the gray value of pixels is convoluted with the Gaussian filter in formula (1), and the results instead of the gray value of pixels are used to calculate further.

$\begin{matrix} {{I\left( {x,y} \right)} = {\sum\limits_{i = \frac{k}{2}}^{\frac{k}{2}}{\sum\limits_{j = {- \frac{k}{2}}}^{\frac{k}{2}}{{F\left( {{x + i},{y + j}} \right)}{g\left( {i,j} \right)}}}}} & (1) \end{matrix}$

F(x,y)—the gray value of the output image,

l(x,y)—the results of the Gaussian convolution, g(i,j)—the coefficient of the Gaussian convolution.

A detailed flow of the method for centroiding for spots is illustrated in FIG. 1.

The steps are follows:

Step 101: First, the gray value of the current pixel is read and saved.

A buffer for the gray value is determined according to the size of a Gaussian convolution template. More specifically, the buffer is determined by the row number. Thus, for example, if the size of the Gaussian convolution template is 7×7, 6 rows are saved once, and processing begins after reading the data of the 7th row.

Step 102˜103: Next, Gaussian convolution to the data in the buffer is performed, and then the result is compared with a predetermined threshold. If the result exceeds the threshold, considering the current pixel as the spot, then the process proceeds to step 104 to identify the spot. If the result does not exceed the threshold, the current pixel is considered as the background, and the process proceeds to step 107.

In the preferred embodiment, the Gaussian convolution is also based on the Gaussian convolution template. For example, if the size of the Gaussian convolution template is 7×7, the image data to be processed includes 7 rows and 7 columns pixels once. Usually, the operations of convolution start at the beginning of the pixel, then scan from left to right and from top to bottom. The convolution is carried out as Formula 1. The threshold is determined by the contrast of the gray value of spots with the background. Usually, the lesser the contrast is the lesser the threshold is, and vice versa.

Step 104: At step 104, the current pixel is marked, and the spots to which the pixels belong are identified.

The background pixels can be marked with zero and the non-background pixels can be marked with non-zero. In applications there are may ways to mark and is limited to the particular method disclosed herein. Rather, the purpose of the marking is to distinguish the background, the non-background and the spots, so a negative integer or a decimal can also be used. Usually, zero and use of a positive integer would be convenience. The steps described below are based on using zero and a positive integer to mark the background and non-background pixels, respectively.

The workflow for marking each pixel is illustrated in FIG. 2.

Step 104 a˜104 b, First, the process judges whether the flag of the left pixel is zero. If so, the process proceeds to step 104 c. If not, the flag of the current pixel is the flag of the left pixel, then the process proceeds to step 104 f.

Step 104 c˜104 e: At step 104 c, the process next judges whether the flag of the upper pixel is zero. If so, the current pixel is marked with a new flag and the new flag value is updated. If the flag of the upper pixel is not zero, the flag of the current pixel is the flag of the upper pixel.

In order to supply the new flag value to the pixel, the new flag value can be saved in a special register. The new flag value can be updated by any way to provide a different value each time. For example, the new flag adds 1 to the new flag value for the next marking operation.

Step 104 f: At step 104 f, the flags of the left and upper pixels are updated with the flag of the current pixel for the next pixel and the next row of pixels.

The flag values of left and upper pixels are saved in a register and a buffer respectively. The left register is initialized to be zero. And the buffer, which saves the flags of pixels in a row, also is initialized to be zero. For example, in a case where there are ten pixels in a row, the buffer will have ten units, with each unit representing a pixel in the row. When the flag of the current pixel is determined, then the flag is saved to the relevant buffer unit. If the current pixel is the 5th pixel in the row, then the flag will be saved to the 5th unit of the buffer. The flag of the upper pixel for marking comes from the buffer.

Step 104 a˜104 f illustrate the process of marking one pixel. The steps 104 a˜104 f are thus repeated for marking all output pixels. For example, as shown in FIG. 3, with respect to the pixel in 2nd row, 4th column, because the flag of the left pixel is zero, then the flag of the upper pixel is zero. Therefore, the pixel is marked as a new flag 2. In respect to the pixel in 2nd row 5th column, because the flag of left pixel is 2, the pixel is directly marked as 2.

Step 105: Referring back to FIG. 1, at step 105, the equivalent flags of the pixels of the same spot are merged together.

FIG. 3 illustrates the image that is marked in step 104. The shaded areas of FIG. 3 are spots, and there are 4 spots in FIG. 3. The pixels of the same spot may have different flags, so these flags are equivalent. In order to unify the flags of all the pixels of the same spot, a method for merging equivalent flags is presented in this disclosure, as shown in FIG. 4. The purpose is to set a same flag of pixels for the same spot. If the background flags of pixels are marked zero, the same values are positive integers starting from 1. The workflow is shown in FIG. 4 and includes the following steps:

Step 105 a˜105 c: At step 105 a, a judgment is made as to whether both of the flags of the left and upper pixels are zero. If so, the corresponding equivalent flag of the current pixel is set as a new one and the new value of equivalent flag is updated. The process then proceeds to step 105 d. If both of the flags of the left and upper pixels are not zero and if the two flags are not equal, a 1 is added to the number of the merging flag and the process then proceeds to step 105 d.

In order to supply a new value of equivalent flags to the pixel, the new value of equivalent flags are saved in the special register. The new value of equivalent flags can be updated by any way to provide a different value each time. For example, the new value of equivalent flag is derived by adding 1 for the next marking. The number of merging flag records the number of equivalent flags which shall be merged, and saves the number in a register. The values of equivalent flag are saved in a buffer.

Step 105 d˜105 h: At step 105 d, a judgment is made as to whether the number of merging flag is 1. If so, the process then marks the left pixel with the equivalent flag of the upper pixel, and then updates the new value of the equivalent flag with the last one. If the step of updating of the new value of the equivalent flag is increasing the flag with 1, the last one is decreasing the flag by 1.

Because the new value of the equivalent flag is updated with the last one on the process of merging the equivalent flags, the range of the equivalent flag value is reduced. Each value of the equivalent flag maps to a data buffer address, so the reduction of the range greatly saves a lot of memory space. In FIG. 3, if the equivalent flag is not merged, it needs 19 buffer units to save all the spots, one flag needs one buffer unit, and lots of memory space is wasted. If the equivalent flag is merged, as shown in FIG. 5, only 4 buffer units are occupied.

If the number of merging flag is not 1, a judgment is made as to whether the value of the equivalent flag of the left pixel is equal to the value of equivalent flag of the upper pixel. If so, no additional action is taken. If the value of the equivalent flag of the left pixel is not equal to the value of the equivalent flag of the upper pixel, the equivalent data and the equivalent flag are merged. In the merging step, the data in the mapping buffer unit of the equivalent flag of the upper pixel is accumulated with the data in the mapping buffer unit of the equivalent flag of the left pixel and the buffer unit of the equivalent flag of the upper pixel mapping is then cleared. And the equivalent flag of the upper pixel is then replaced by the equivalent flag of the left pixel.

FIG. 5 illustrates the result of merging of the information from FIG. 3. The flags of the pixels in FIG. 5 are the real addresses in the buffer. For example, the flag of the pixel at the top left corner is 1, which means the data of the same spot with flag 1 is saved in the buffer unit which the address is 1.

In some applications, it is not necessary for the step of merging if all the pixels of the same spot have the same flag and the memory space is enough. Thus, step 105 is optional.

Step 106. At step 106, the product of the gray value of the pixel and the coordinate value of the same spot is accumulated. At the same time, the gray value of the same spot is accumulated and the results of the accumulating steps are saved, respectively. The process then proceeds to step 110.

In present disclosure, step 104, step 105 and step 106 can be done as parallel processes. Therefore the speed of processing can be improved greatly.

Step 107: In step 107, the pixel is marked with a background flag. In one embodiment, the background pixels are marked with zero; then the flag of the left and the upper pixel are cleared.

Step 108˜109: In step 108, a judgment is made as to whether the flag of the left pixel exceeds zero. If so, the data storage of the spot to which the pixel belongs is adjusted. The detail of adjustment step is as follows: First, the value in accumulator is added to the data in buffer which maps to the value of the equivalent flag. Next, the accumulator is cleared. if the flag of the left pixel does not exceed zero, then the process proceeds to step 110.

Step 110: In step 110, a judgment is made as to whether all pixels of the image has been disposed completely. If so, the process proceeds to step 111. If all of the pixels have not been disposed of completely, to the process returns to step 101. A flag is set as an end indicator.

Step 111: At step 111, according to the Formula 2 below, the accumulation of the products of the gray value of pixels and coordinates by the accumulation of gray value of pixels is divided, and the quotient is outputted as the centroid coordinates of the spot.

$\begin{matrix} {{x_{0} = \frac{\sum\limits_{x = 1}^{n}{\sum\limits_{y = 1}^{m}{{I\left( {x,y} \right)}x}}}{\sum\limits_{x = 1}^{n}{\sum\limits_{y = 1}^{m}{I\left( {x,y} \right)}}}}{y_{0} = \frac{\sum\limits_{x = 1}^{n}{\sum\limits_{y = 1}^{m}{{I\left( {x,y} \right)}y}}}{\sum\limits_{x = 1}^{n}{\sum\limits_{y = 1}^{m}{I\left( {x,y} \right)}}}}} & (2) \end{matrix}$

In Formula 2, l (x, y) is the gray value of the pixel under the Gaussian convolution. x0 and y0 are the centroid coordinates of the spot.

In order to implement this method real-time, a spot centroiding system is presented in this disclosure. As shown in FIG. 6, the system comprises: a spot identifying unit 61, a Gaussian filtering unit 62 and a spot centroid computing unit 63. The spot identifying unit 61 receives the control signal which is inputted from a threshold comparator 632 of the spot centroid computing unit 63, and marks pixels of the spots image, and merges the equivalent flags of the same spot. The spot identifying unit 61 further comprises: a mark arbiter 611, a left flag register 613, an upper flag buffer 614, a current flag register 615 and a new flag register 616, an arbiter of the equivalent flag merger 612, a merging flag register, 617, a new equivalent flag register 618 and an equivalent flag buffer 619.

The mark arbiter 611 marks the pixels with the left flag register 613, the upper flag buffer 614, the current flag register 615 and the new flag register 616, the flow as shown in FIG. 2.

The arbiter of equivalent flag merger 612 merges the equivalent flags of same spot with the left flag register 613, the upper flag buffer 614, the merging flag register, 617, and the new equivalent flag register 618, as shown in the detailed flow in FIG. 4. The merging results are saved in the equivalent flag buffer 619.

The current flag register 615, the left flag register 613, the upper flag buffer 614, the new flag register 616, the merging flag register, 617, the new equivalent flag register 618 and the equivalent flag buffer 619 provide the current flag, the left flag, the upper flag, the new flag, the number of equivalent flags which shall be merged, new equivalent flag and equivalent flag to the mark arbiter 611 and the arbiter of equivalent flag merger 612. The upper flag buffer 614 and the equivalent flag buffer 619 are configured for saving a group of flags, rather than for saving a single flag. The equivalent flag buffer 619 sends equivalent flags merged as the address to data buffers 635 a, 635 b and 635 c.

If the merging is not needed, the arbiter of equivalent flag merger 612, the merging flag register 617, the new equivalent flag register 618 and the equivalent flag buffer 619 can be omitted.

The Gaussian filtering unit 62 is configured for convoluting the gray value of the pixel with Gaussian filter and transferring the result thereof to the spot centroid computing unit 63. The Gaussian filtering unit 62 further comprises an image buffer 621 and a Gaussian convolution unit 622. The image buffer 621 is configured for saving the gray value of the pixel temporarily and sending the gray value to the Gaussian convolution unit 622. The Gaussian convolution unit 622 is configured for doing the Gaussian convolution of the gray value of the pixel and sending the result thereof to a threshold comparator 632, multipliers 633 a and 633 b, and an accumulator 634 c of the spot centroid computing unit 63.

The spot centroid computing unit 63 is configured for calculating the centroid of the spots image, then outputting the final result. The spot centroid computing unit 63 further comprises a row and column counter 631 for calculating and supplying a coordinate value of each pixel and providing an x and y coordinates value of each pixel to multipliers 633 a and 633 b respectively. The spot centroid computing unit further comprises the threshold comparator 632 for comparing results from the Gaussian convolution unit 622 with the predetermined threshold and then outputting the result of that comparison as the control signal to the mark arbiter 611, the arbiter of equivalent flag merger 612, and the accumulator 634 a, 634 b and 634 c.

The spot centroid computing unit 63 further comprises multipliers 633 a and 633 b, accumulators 634 a, 634 b and 634 c, the data buffers 635 a, 635 b and 635 c, and dividers 636 a and 636 b. The multipliers 633 a, 633 b are configured for receiving the results of the Gaussian convolution unit 622 and the x and y coordinates from the row and column counter and outputting the product of the gray value of pixel and the coordinate value. The accumulators 634 a, 634 b and 634 c are configured for receiving the outputting result from the threshold comparator 632 and outputting the accumulation of itself and accumulating the result from the multipliers 633 a, 633 b and the Gaussian convolution unit 622. Actually, the multiplier 633 a and the accumulator 634 a are configured for accumulating of the product of the gray value of pixels with an x coordinate value of the same spot, and saving the computed results in the data buffer 635 a. The multiplier 633 b and the accumulator 634 b are configured for accumulating of the product of the gray value of pixels with a y coordinate value of the same spot, and saving the results thereof in the data buffer 635 b.

The accumulator 634 c is configured for accumulating the gray value of all pixels of the same spot, and saving the results in the data buffer 635 c. The dividers 636 a and 636 b are respectively configured for calculating the quotient between the accumulation of the product of the gray value of pixels and x coordinate values and the accumulation of gray value of pixels and calculating the quotient between the accumulation of the product of the gray value of pixels and y coordinate values and the accumulation of gray value of pixels. Next, the dividers get the x and y coordinates of spot centriod. The multipliers 633 a and 633 b, the accumulator 634 a, 634 b and 634 c, the data buffer 635 a, 635 b and 635 c, the divider 636 a and 636 b are used to realize the calculation in formula 2.

The spots image centrioding system in this disclosure can be implemented by a field programmable gate array (“FPGA”) or an application specific integrated circuit (“ASIC”).

To locate a spot centriod, the system shown in FIG. 6 receives the gray value of pixels from a sensor, and saves the gray value in image buffer 621. Next, the gray value of pixels in image buffer 621 is sent to the Gaussian convolution unit 622 to realize Gaussian convolution and implement the Gaussian filtering. The result of the Gaussian convolution is inputted to the threshold comparator 632, which is compared with the predetermined threshold. Then, the threshold comparator 632 judges as to whether to carry out spot identification according to the compared results. If the comparator indicates that that spot identification should proceed, the threshold compared results are inputted into the mark arbiter 611 and the arbiter of equivalent flag merger 612 in the spot identifying unit 61 as a control signal, and the system starts to mark the spot image and merge equivalent flag. The detailed process of marking and merging are accomplished with the mark arbiter 611, the left flag register 613, the upper flag buffer 614, the current flag register 615 and the new flag register 616, the arbiter of equivalent flag merger 612, the merging flag register 617, the new equivalent flag register 618 and the equivalent flag buffer 619 according to the process flow as shown in FIG. 2 and FIG. 4. At the same time, accumulation of the product of the gray value of pixel and coordinate values and accumulation of the gray value of pixel and storage of the results are accomplished by the multipliers 633 a and 633 b, the accumulators 634 a, 634 b and 634 c, and the data buffers 635 a, 635 b and 635 c. When whole pixels of the image are processed, the x and y coordinate values of spot centroid are computed by dividers 636 a and 636 b. Then, x and y coordinate values of each pixel are provided by the row and column counter 631.

The advantages of the presented representative embodiment are as follows:

1) Gaussian weighing centroiding is introduced in this disclosure, which is, doing Gaussian convolution to the gray value of output pixel, then identifying the spots. Using this method, the ability of noise-resistance is improved and high precision is realized.

2) Each pixel is marked and disposed of correspondingly in this disclosure instead of being limited to a window, so all spots in the image can be identified and disposed of and the size and shape of spots are not restricted.

3) The same spot may have more than one equivalent flag, so the data of the spot may occupy more than one memory space. Therefore, in this disclosure equivalent flags of the same spot are merged when the pixels are marked. The data of the same spot is saved in the same memory space, so the spaces of memory are saved greatly.

4) The processing of marking pixels, merging equivalent flags, and calculating the centroid are done in parallel and implemented with FPGA (Field Programmable Gate Array) hardware, so the update rate can reach 30 MHz which enables real-time spots centrioding.

The foregoing description of various embodiments of the invention has been present for purpose of illustration and description. It is not intent to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed where chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled. 

1. A rapid and high precision centroiding method for spots image comprising: A. convoluting the gray value of a pixel with a Gaussian filter and judging whether the result the gray value calculation exceeds a predetermined threshold, and if so, then proceeding to step B, and if not, then proceeding to step C; B. marking a current pixel with a flag to identify which spot the current pixel belongs to, then accumulating a product of the gray value and a coordinate value of the same spot; and at the same timer accumulating the gray value of the same spot; saving the results of the accumulations, respectively, and proceeding to step D; C. marking the current pixel as a background flag, then judging whether data in a buffer needs to be adjusted, and if so, then adjusting the data in the buffer, and if not, then proceeding to step D; D. judging whether all pixels of the image have been disposed of completely, and if not, then returning to step A, and if so then calculating a quotient of the accumulations of the product of the gray value and the coordinate value and the accumulations of the gray value, outputting the quotients as the coordinates value of the centroid of each spot image.
 2. The rapid and high precision centroiding method for spots image according to claim 1, wherein step B further comprises: merging the equivalent flags of the same spot when marking.
 3. The rapid and high precision centroiding method for spots image according to claim 1, further comprising reading the gray value of the current pixel and saving it in the buffer prior to performing the step of convoluting the gray value of a pixel with a Gaussian filter.
 4. The rapid and high precision centroiding method for spots image according to claim 1, wherein the step of marking the current pixel further comprises: B11. judging whether the flag of the left pixel is zero, and if so, then proceeding to step B12, and if not, then marking the pixel with the flag and then proceeding to step B13; B12. judging whether the flag of the upper pixel is not zero, and if so, marking the current pixel with the flag of the upper pixel, then proceeding to step B13, and if not, marking the current pixel with a new flag, then updating the new flag value; and B13. updating the flags of the left and upper pixels with the flag of the current pixel.
 5. The rapid and high precision centroiding method for spots image according to claim 2, wherein the step of merging equivalent flags of the same spot further comprises: B21: judging whether both of the flags of the left and upper pixels are zero, and if so, setting a corresponding equivalent flag of the current pixel as a new flag, then updating the new value of the equivalent flag and proceeding to step B22, and if the flags of the left and upper pixels are not zero and are also not equal, then adding 1 to the number of the merging flag, and proceeding to step B22; B22: judging whether the number of the merging flag is 1, and if so, marking the left pixel with the equivalent flag of the upper pixel, then updating the new value of the equivalent flag to the last one, and if not, proceeding to step B23; B23: judging whether the value of equivalent flag of the left pixel is equal to the value of equivalent flag of the upper pixel, and if so, doing nothing, and if not, then merging the equivalent data and marking the equivalent flag of the upper pixel with the equivalent flag of the left pixel.
 6. The rapid and high precision centroiding method for spots image according to claim 1, wherein step C further comprises: clearing the flags of the upper pixel and left pixel; and wherein the judging in the step C further comprises: judging whether the flag of the left pixel exceeds zero, if so, then adjusting the data in the buffer which belongs to the same spot of the current pixel, and if not, making no adjustment; wherein the step of adjustment comprises: accumulating the value in the accumulator with the data in the buffer which is corresponding to the value of equivalent flag of the pixel and then clearing the accumulator.
 7. A rapid and high precision centroiding system for spots image comprising: a Gaussian filtering unit; a spot identifying unit; and a spot centroid computing unit, wherein the Gaussian filtering unit is configured for convoluting a gray value of a pixel for the spot's image with a Gaussian filter and transferring the result thereof to the spot centroid computing unit; wherein the spot identifying unit is configured for receiving a control signal, which is inputted from the spot centroid computing unit, and marking pixels of the spots image; wherein the spot centroid computing unit is configured for calculating the centroid of a spot's image according to the flags of the pixels, then outputting the final result.
 8. The rapid and high precision centroiding system for spots image according to claim 7, wherein the spot identifying unit further comprises: a mark arbiter; a left flag register; an upper flag buffer; a current flag register; and a new flag register; wherein the mark arbiter is configured for marking the pixels; wherein the left flag register is configured for saving and sending the flag of the left pixel to the mark arbiter; wherein the upper flag buffer is configured for saving and sending the flag of the upper pixel to the mark arbiter; wherein the current flag register is configured for saving and sending the flag of the current pixel to the mark arbiter; and wherein the new flag register is configured for saving and sending the new flag of the current pixel and supplying it to the mark arbiter.
 9. The rapid and high precision centroiding system for spots image according to claim 8, wherein the spot identifying unit further comprises an arbiter of an equivalent flag merger, a merging flag register, a new equivalent flag register and an equivalent flag buffer; wherein the arbiter of the equivalent flag merger is configured for merging equivalent flags of the same spot; wherein the merging flag register is configured for saving the number of equivalent flags that shall be merged; wherein the new equivalent flag register is configured for sending the new value of equivalent flag to the arbiter of the equivalent flag merger; and wherein the left flag register and the upper flag buffer further are configured for supplying the flag value of left pixel and the flag value of upper pixel, respectively, to the arbiter of equivalent flag merger for judgment.
 10. The rapid and high precision centroiding system for spots image according to claim 7 wherein the Gaussian filtering unit further comprises an image buffer and a Gaussian convolution unit; wherein the image buffer is configured for saving the gray value of the pixel temporarily and sending saved gray values to the Gaussian convolution unit; and wherein the Gaussian convolution unit is configured for calculating the gray value of the pixel with a Gaussian convolution and sending the result thereof to the spot centroid computing unit.
 11. The rapid and high precision centroiding system for spots image according to claim 7 wherein the spot centroid computing unit further comprises: a row and column counter configured for calculating and supplying a coordinate value of each pixel; a threshold comparator configured for comparing the result from the Gaussian convolution unit with a predetermined threshold, then outputting the result of that comparison as the control signal; a first multiplier configured for calculating a product of the gray value and an x coordinate value of the pixel and a second multiplier for calculating the product of the gray value and a y coordinate of the pixel; a first accumulator configured for accumulating the product of the gray value and the x coordinate value of the pixel and a second accumulator for accumulating the product of the gray value and the y coordinate value of the pixel, wherein the first and second accumulators are configured to send the results of the two accumulators to first and second data buffers, separately; a third accumulator configured for accumulating the gray value of the pixel and sending the result to a third data buffer; wherein the first, second and third data buffers are configured for saving the result of the first, second and third accumulators separately; and a first divider configured for calculating the quotient of the value in the first data buffer and the third data buffer and a second divider for calculating the quotient of the value in the second data buffer and the third data buffer. 